Most cancer patients succumb to their malignancy as a result of metastatic invasion. The process which tumor cells undergo metastasis involves multiple steps and consequently, metastasis can be promoted by several mechanisms. A greater understanding of these mechanisms might result in novel and effective therapies to prevent metastatic invasion. Studies that are proposed in this project are aimed at delineating the mechanism(s) by which tissue factor (TF) promotes metastasis. TF is a transmembrane glycoprotein with procoagulant activity that is expressed in high levels on many tumor cells. Preliminary studies suggest that a high level of TF expression on human melanoma cells can increase their metastatic potential using an in vivo model of hematogenous metastasis. The studies proposed are designed to determine whether metastasis is facilitated by the procoagulant activity of TF or whether mechanisms other than activation of blood coagulation are operating. These studies will utilize retroviral vectors to alter TF expression as well as express mutant forms of TF in a human melanoma cell line. Metastatic potential of these melanoma cells will be determined with an in vivo model of metastasis using immunocompromised mice. Initial studies will be aimed at determining whether the extracellular domain of TF (involved in activation of blood coagulation) and/or the cytoplasmic domain of the molecule is involved in facilitating metastasis using transfected melanoma cells that express mutant forms of TF. Further studies will determine the role of thrombin, fibrin, and phosphorylation of the cytoplasmic domain of TF in mediating the prometastatic effect of IF using an in vivo model of metastasis. The possibility that TF might promote the interaction of tumor cells and endothelium/subendothelial matrix, critical steps in hematogenous metastasis, will also be determined using in vivo models of' tumor cell-endothelium/subendothelial matrix interaction. These in vivo models will involve high and low TF expressing melanoma cell clones and their attachment to the umbilical vein endothelial cells, transmigration across endothelium, attachment to subendothelial matrix and invasion of subendothelial matrix.